Question

(a) A type of single pulley is very often used as a machine even though it does not give any mechanical advantage. (i) Name the type of pulley used. (ii) For what purpose is such a pulley used?
(b) Can a simple machine act as a force multiplier and a speed multiplier at the same time?
(c) A block and tackle system of pulleys has a velocity ratio of $4$. (i) Draw a labeled diagram of the system indicating clearly the points of application and directions of load and effort. (ii) What is the value of the mechanical advantage of the given pulley system if is an ideal pulley system?

(ICSE Exam. $2013$)

Answer 1

(a)
(i) Single fixed pulley is the type of single pulley which is very often used as a machine even though it does not give any gain in mechanical advantage.
(ii) Single fixed pulley is used only to change the direction of the force applied.
(b) It is not possible for a machine to act as a force multiplier and speed multiplier simultaneously. This is because machines which are force multipliers cannot gain in speed and vice-versa.
(c)
(i)The labeled diagram of the system of block and tackle system of pulleys is shown indicating clearly the points of application and direction of load and effort. Since the $\text{VR}=4$, the number of pulleys$=4$ for a block and tackle system.
(ii) Given:
Velocity ratio, $\text{VR}=4$,
Load $=4T$,
Effort $=T$
Mechanical advantage, $\text{MA}=\frac{\text{Load}}{\text{Effort}}$
$=\frac{4T}{T}=4$

Hence, the mechanical advantage of the given pulley system is $4$.